1. Field of the Invention
The present invention relates to a transmitted light attenuation measuring method in which a variation of the quantity of light when passing through blood flowing through an artery of a living body, which is caused by light absorptive materials in the blood, is detected and oxygen saturation, cardiac output and blood volumes, and the like in the blood are obtained on the results of the detection, and a photo sensor used for the measurement. More particularly, the invention relates to a blood transmitted light attenuation measuring method for detecting light transmitted through a superficial temporal artery region, and a photo sensor used for the measurement.
2. Related Art
A probe for the photo sensor is known for the probe used in a pulsative wave spectral measuring method for measuring oxygen saturation in blood of a living body and cardiac output and blood volumes by injecting a dye into blood. The known probe is attached to an ear lobe, a concha, or a finger tip of the living body. A light emitting piece as a light emitting means, such as a LED, projects rays of light into the body of the living body. Light transmitted therethrough is received by a photo sensing piece as a photo sensing means, such as a Photo Diode. Light absorptive material in blood flowing through an artery in tissue near to its mounting portion is detected on the basis of the received light.
The attachment of the probe to an ear lobe, a concha, or a finger tip of the living body is easy. When it is attached to the finger tip, a pulsative wave signal of a large amplitude can be obtained. When the motive nerves of the blood vessel are stimulated by a nerve reflection caused by deep breathing or injection liquid, the blood flow varies, so that the measurement is instable.
When the probe is attached to the ear, the measurement is little affected by the vessel contraction owing to the nerve reflection, but the amplitude of the pulsative wave signal is small. For this reason, it is difficult to obtain a stable measurement particularly for ICU patients during the anesthesia or after the operation.
When the cardiac output and blood volumes are measured by injecting the dye into blood, blood flow is impeded as the result of attaching the probe. This leads to deterioration of measurement accuracy and the reproducibility. In the clip setting applied to the ear lobe, the probe is easily moved when the subject moves. This results in instable measurement and great measurement errors.